Inuyasha series ended in a cliffhanger
but the manga finished it (FINALLY)
had to read 200+ chapters from where
the anime left off -_-
and to those interested u can read the
whole inuyasha manga on onemanga.com

Anime that pissed me off the most since it was never completed: Groove Adventure Rave. Really made me disappointed...Ichigo100% is another. There's also Suzuka, Spiral, Air Gear, Claymore, Tenjo Tenge, Shaman King, and others I'm too lazy to mention.